SensorDirectChannel

public final class SensorDirectChannel
extends Object implements Channel

java.lang.Object
   ↳ android.hardware.SensorDirectChannel


Class representing a sensor direct channel. Use createDirectChannel(android.os.MemoryFile) or createDirectChannel(android.hardware.HardwareBuffer) to obtain an object. The channel object can be then configured (see configure(Sensor, int)) to start delivery of sensor events into shared memory buffer.

Summary

Constants

int RATE_FAST

Sensor operates at nominal rate of 200Hz.

int RATE_NORMAL

Sensor operates at nominal rate of 50Hz.

int RATE_STOP

Sensor stopped (no event output).

int RATE_VERY_FAST

Sensor operates at nominal rate of 800Hz.

int TYPE_HARDWARE_BUFFER

Shared memory type wrapped by HardwareBuffer object.

int TYPE_MEMORY_FILE

Shared memory type ashmem, wrapped in MemoryFile object.

Public methods

void close()

Close sensor direct channel.

int configure(Sensor sensor, int rateLevel)

Configure sensor rate or stop sensor report.

boolean isOpen()

Determine if a channel is still valid.

Protected methods

void finalize()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

Inherited methods

Constants

RATE_FAST

added in API level 26
int RATE_FAST

Sensor operates at nominal rate of 200Hz. The actual rate is expected to be between 55% to 220% of nominal rate, thus between 110Hz to 440Hz.

Constant Value: 2 (0x00000002)

RATE_NORMAL

added in API level 26
int RATE_NORMAL

Sensor operates at nominal rate of 50Hz. The actual rate is expected to be between 55% to 220% of nominal rate, thus between 27.5Hz to 110Hz.

Constant Value: 1 (0x00000001)

RATE_STOP

added in API level 26
int RATE_STOP

Sensor stopped (no event output).

Constant Value: 0 (0x00000000)

RATE_VERY_FAST

added in API level 26
int RATE_VERY_FAST

Sensor operates at nominal rate of 800Hz. The actual rate is expected to be between 55% to 220% of nominal rate, thus between 440Hz to 1760Hz.

Constant Value: 3 (0x00000003)

TYPE_HARDWARE_BUFFER

added in API level 26
int TYPE_HARDWARE_BUFFER

Shared memory type wrapped by HardwareBuffer object.

Constant Value: 2 (0x00000002)

TYPE_MEMORY_FILE

added in API level 26
int TYPE_MEMORY_FILE

Shared memory type ashmem, wrapped in MemoryFile object.

Constant Value: 1 (0x00000001)

Public methods

close

added in API level 26
void close ()

Close sensor direct channel. Stop all active sensor in the channel and free sensor system resource related to channel. Shared memory used for creating the direct channel need to be closed or freed separately.

configure

added in API level 26
int configure (Sensor sensor, 
                int rateLevel)

Configure sensor rate or stop sensor report. To start event report of a sensor, or change rate of existing report, call this function with rateLevel other than RATE_STOP. Sensor events will be added into a queue formed by the shared memory used in creation of direction channel. Each element of the queue has size of 104 bytes and represents a sensor event. Data structure of an element (all fields in little-endian):

   offset   type                    name
 ------------------------------------------------------------------------
   0x0000   int32_t                 size (always 104)
   0x0004   int32_t                 sensor report token
   0x0008   int32_t                 type (see SensorType)
   0x000C   uint32_t                atomic counter
   0x0010   int64_t                 timestamp (see Event)
   0x0018   float[16]/int64_t[8]    data (data type depends on sensor type)
   0x0058   int32_t[4]              reserved (set to zero)
 
There are no head or tail pointers. The sequence and frontier of new sensor events is determined by the atomic counter, which counts from 1 after creation of direct channel and increments 1 for each new event. Atomic counter will wrap back to 1 after it reaches UINT32_MAX, skipping value 0 to avoid confusion with uninitialized memory. The writer in sensor system will wrap around from the start of shared memory region when it reaches the end. If size of memory region is not a multiple of size of element (104 bytes), the residual is not used at the end. Function returns a positive sensor report token on success. This token can be used to differentiate sensor events from multiple sensor of the same type. For example, if there are two accelerometers in the system A and B, it is guaranteed different report tokens will be returned when starting sensor A and B. To stop a sensor, call this function with rateLevel equal RATE_STOP. If the sensor parameter is left to be null, this will stop all active sensor report associated with the direct channel specified. Function return 1 on success or 0 on failure.

Parameters
sensor Sensor: A Sensor object to denote sensor to be operated.

rateLevel int: rate level defined in SensorDirectChannel.

Value is either 0 or combination of RATE_STOP, RATE_NORMAL, RATE_FAST or RATE_VERY_FAST.

Returns
int * starting report or changing rate: positive sensor report token on success, 0 on failure; * stopping report: 1 on success, 0 on failure.

Throws
NullPointerException when channel is null.

isOpen

added in API level 26
boolean isOpen ()

Determine if a channel is still valid. A channel is invalidated after close() is called.

Returns
boolean true if channel is valid.

Protected methods

finalize

added in API level 26
void finalize ()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. A subclass overrides the finalize method to dispose of system resources or to perform other cleanup.

The general contract of finalize is that it is invoked if and when the Java™ virtual machine has determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, except as a result of an action taken by the finalization of some other object or class which is ready to be finalized. The finalize method may take any action, including making this object available again to other threads; the usual purpose of finalize, however, is to perform cleanup actions before the object is irrevocably discarded. For example, the finalize method for an object that represents an input/output connection might perform explicit I/O transactions to break the connection before the object is permanently discarded.

The finalize method of class Object performs no special action; it simply returns normally. Subclasses of Object may override this definition.

The Java programming language does not guarantee which thread will invoke the finalize method for any given object. It is guaranteed, however, that the thread that invokes finalize will not be holding any user-visible synchronization locks when finalize is invoked. If an uncaught exception is thrown by the finalize method, the exception is ignored and finalization of that object terminates.

After the finalize method has been invoked for an object, no further action is taken until the Java virtual machine has again determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, including possible actions by other objects or classes which are ready to be finalized, at which point the object may be discarded.

The finalize method is never invoked more than once by a Java virtual machine for any given object.

Any exception thrown by the finalize method causes the finalization of this object to be halted, but is otherwise ignored.

Throws
Throwable